Is grid connectivity inverter really worth it?
- Thread starter Alkaline
- Start date
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,682
35% greater panel cost but 200% greater mounting hardware?
Differences between the two proposed systems.
Is there an analysis of your consumption to support battery size?
$6000 could be 3 or 4 server rack batteries, 15kWh to 20kWh.
Whether with batteries or zero-export grid-tie, would ideally have variable loads to use power when it is made.
Not many continuously variable loads are available. PV direct Grundfos pump would be, but when tank is full the PV sits idle. Powered from the system but controlled to use surplus would be ideal.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,682
The Growatt transformers have some switching trying to make the 240V inverter + auto-transformer + grid work together.
It's pretty easy to exceed 2500W or 5000W of 120V load. A house has many 120V circuits and appliances. Dishwasher, clothes washer, garbage disposer, coffee pot, microwave, hair dryer, refrigerator's defroster & ice maker ...
If 6x 240V inverter, a large isolation transformer might be the way to go. But transformers meant for the grid aren't a nice load for inverters.
Think he said the grid panels were feeding inverters and charging batteries.
Zwy
Solar Wizard
I cycle lightly, the larger bank makes up for charging to 95% or less, I go just over 3.4V when charging in order to engage balancing.Your calculation for batteries is $0.0264/kWh. My rough number was $0.05/kWh. That changes the PV panel to battery calculation a bit.
Most commercial battery systems are much more expensive, but DIY with cells and server rack batteries might reach this range.
All based on manufacturer's claimed cycles. There are a few forum members with actual experience of high cycle life. Many more with failure?
Tests have not shown many manufacturers reaching claimed life. Those were operated around 1C continuously, so results may be better with our gentle cycling.
Are LFP prices artificially high?
Cost is irrelevant to sale price. market value is king. profit drawn from building, marketing, future sale reduction pricing, etc. I would be EXTREMELY surprised if sales were anywhere close to material and labor and manufacturing costs... It's like the cannabis market. It costs MAYBE $50 to...diysolarforum.com
I don't like putting a lot of money into chemistry that degrades with time.
Electronics, I think main degradation mechanism comes from electrolytic capacitors and semiconductors, both strongly affected by temperature.
I have some experience with electronics still operating decades later.
Fans, of course, need replacement. I just ordered a 24V fan for VFD that I've had for 20 years.
For grid-backup batteries I went with AGM 3 years ago. 1/5th the cost of lithium (that I knew about) for 1/5th the cycle life.
If I get pushed onto NEM 3.0 I'll consider changing that system to LiFePO4 and moving the AGM to another system on NEM 2.0
I might get 2500 cycles or I might get 10K cycles. Even with 2500 cycles, I only fully cycle about every 4 days. That might outlast me.
I needed a place to park what I earn in a year, I have no debt and thus can freely invest most of what I earn. I figured this will easily beat inflation as long as I'm alive, the side benefit was I didn't need a standby generator which I was considering for a few years. In this area with my utility and 1:1 net metering, I can only bank 500Kwh on the grid, they get the excess for free. At true up, they don't give credit or pay. Grid tie for me was not a great option.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,682
Meaning you can only stuff 1.37 kWh into grid and put out of grid each day, on average, for 500 kWh of yearly storage?
Or, the grid has "only" 500 kWh capacity you can use (e.g. bank in the summer to use in winter)?
At 4 days per cycle, 2500 cycles will take 27 years. Some lithium batteries indicate 30 year design life.
Your avoiding frequent full charge should help.
Do they stay at moderate temperature? Consider A/C if needed.
Also maybe some way to monitor for hot connections (BMS detecting cell divergence might do.)
I imagined PTC fuses stuck on every terminal, connected in series with contactor.
One guy wired a smoke alarm in his battery room to shut system off, although that didn't stop a failure in his case.
Electricity we can live without. Water we can't. Do you have a tank, to get by when well pump is out of service?
(I should set up a tank, but I do have a pool.)
Or, the grid has "only" 500 kWh capacity you can use (e.g. bank in the summer to use in winter)?
At 4 days per cycle, 2500 cycles will take 27 years. Some lithium batteries indicate 30 year design life.
Your avoiding frequent full charge should help.
Do they stay at moderate temperature? Consider A/C if needed.
Also maybe some way to monitor for hot connections (BMS detecting cell divergence might do.)
I imagined PTC fuses stuck on every terminal, connected in series with contactor.
One guy wired a smoke alarm in his battery room to shut system off, although that didn't stop a failure in his case.
Electricity we can live without. Water we can't. Do you have a tank, to get by when well pump is out of service?
(I should set up a tank, but I do have a pool.)
Zwy
Solar Wizard
At any time, the bank is limited to 500Kwh. You can produce it in summer and use it in winter. Most grid tie around here is at 47 degrees and the snow sits on panels for weeks at a time. Most report the bank is used up mid January.
In my basement, battery cells never above 23C.
I use a Batrium CORE with K9's, long term I think it is the way to go.
I thought about a warning system but with the large metal utility cabinet housing the bank, I'm not overly concerned.
I have a well, powered entirely by my solar system. If my pump goes out, I could always go to the neighbors 150 feet away and get water from their well.
People out here in Timbuktu, IA are pretty self sufficient. My parents winter in TX and when the winter storm hit a few years back, it wasn't a big deal for them having lived here thru long cold winters. Water came from the ocean to flush toilets (filled the bath tub for reserve), heat was the LP gas stove and light to play cards was from a white gas lantern. Refrigeration was ice from a convenience store that was giving ice away as they couldn't keep it. They don't have solar there, but they managed, no big deal for them. Meanwhile neighbors were all freaking out and saying it was the end of the world.
I grew up when power was out running a tractor PTO to pump water with a pump jacket well (livestock need plenty of water), and using tractor engine vacuum to run milking machines. White gas lanterns for light and cooking on a gas stove. Heat was the wood furnace with manual draft and let the hot air rise up the ducts (house was only heated with wood, we never used gas).
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,609
That's what I thought, until the end of the video. lol
With off grid I can build a diy mounting system. With grid tie the system has to be signed off in by the PE and he will only sign engineered systems like iron ridge $$$
If I use 1500 a month and self consume 750 during solar hours then to zero out my bill I would need battery capacity for 750kwh in the month or about 25kwh a day. So that's where I get my $6000 30kwh diy bank.
I forgot about kitchen loads lol
How's he feeding a 230v only inverter from us grid. Isn't that supposed to create a dead short?
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,609
Not a short. But N/G bonding issues. And possibly grid balancing issues.
Ok. I like that system if there is no grid connection
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,609
It's pretty close to what I will have. If I ever get it finished. lol
What are you waiting on lol.
cs1234
Solar Wizard
- Joined
- May 9, 2022
- Messages
- 2,302
I had a forced week of no electricity or running water during the ice storm here in Texas. We were burning whatever random stuff we could find for warmth and to heat food. Since then, mine is more tolerant of tom foolery when it comes to electricity generation.
If I had known about just charging the battery with something like a chargeverter and not connecting the grid to the inverter I probably would have gone this route. Or bought one of those deyes that was in the classified section a while back
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,682
Sounds like net metering is worthwhile then. Cheaper than a battery. Just can't supply 100% of your winter power. Is that resistance heating, or heat pump?
For a single day's use, you may not need to store a day's use in battery. Just one night's use.
Would that be about 1/3 of 25kWh? Or more? Maybe you only need 8kW ~ 10kW to get by when the grid is down. Not including winter heat. Run well pump when battery is full, filling a tank.
Grid would make that practical, taking care of days without sun.
My usable capacity of battery is close to 1 hour's effective sun. It should make it through the night powering my inefficient old refrigerators, but only if not powering yard lights and an old tube amplifier.
Zwy
Solar Wizard
It gets cold here. Heating in spring/fall can be done with a heat pump. LP gas is king followed by wood heat.
There are those that have ground source heat pump but I don't know of any that really have solar.
Net metering is not worth it here, they already changed the rules governing the what used to be the local coop utility. After farmers installed arrays and had been on net metering. You can't win over the long haul with grid tie here, it's a moving target.
My bank can power my house for 4 days easily if we cut usage to a minimum without any PV input. This is the smart way of handling PV power, on sunny days the bank gets built up and depleted on days with hardly any yield. The bank can handle that.
This isn't CA, it snows here and then gets cold so those grid tie owners with fixed angle arrays don't get any yield for most of the winter months. Snow won't slide off when the temps are -20F. If you put the figures together on how long it takes to get the original cost back, you will find most take 15 years. Meanwhile, I get mine back in half that time and that includes the battery.
I use about 50kwh a day but about half of that is when the sun is shining so I don't need to store that in batteries but I could store the other half. I don't have to of course, I could also use less battery and offset less of my consumption. I still have a few months of data to gather before I make the final decision
Similar threads
